It is known that 10 Gbit InfiniBand is only capable of reaching approximately 10 km due to the limit within the InfiniBand Architecture of at most 128 KiB of granted credits per virtual lane (VL). This restriction places an upper limit on the amount of data that can be in transit at once, since a standard InfiniBand transmitter will not transmit without an available credit. Further, it is known that limiting the amount of data that can be in transit to less than the bandwidth latency product of a network path will directly limit the maximum data transfer rate that can be attained.
For instance, a 10 Gbit InfiniBand link with a round trip latency of 130 microseconds has a bandwidth latency product of 128 KiB, which is the maximum amount of credits that can be granted for a single VL within an InfiniBand link.
Typically an InfiniBand link will have more than 1 ingress and egress VL (up to 15), which the InfiniBand Architecture specifies must each be independently buffered and flow controlled to prevent head of line blocking and flow control dead lock. In some embodiments, the InfiniBand interface contains additional flow control buffering units to transition from a WAN clock domain to an InfiniBand clock domain.
Due to physical limitations data travels at a rate slower than the speed of light over optical fiber. When the fiber is considered as a conduit that carries bits, it is clear that a single piece of long fiber may contain many megabits of data that is in transit. For instance, if the speed of light in a particular fiber carrying a 10 Gbit data stream is 5 ns/meter and the fiber is 100 km long then the fiber will contain 5 megabits of data in each direction. Many WAN paths also include added latency from in band equipment such as regeneration equipment, optical multiplexes, add/drop multiplexors, routers, switches and so on. This extra equipment adds additional latency and further extends the bandwidth latency product of the path.
As defined by the InfiniBand Architecture the InfiniBand electrical and optical signaling protocols are not compatible with, or suitable for use in, a traditional WAN environment. Typical WAN environments use the Synchronous Optical Network (SONET) standard over long distance optical fiber.
Also to ease administration of the InfiniBand network it is desirable to perform routing on InfiniBand packets, as described in the InfiniBand Architecture. Routing allows each remote distant site to maintain local control over their portion of the larger InfiniBand network without imposing substantial policy on all other participants.